Device for simultaneously tuning oscillatory circuits



DEVICE FOR SIMULTANEOUSLY 'TUNING OSCILLATORY CIRCUITS Filed July 22, 1941 45y fflnzmf /77 roan 5y Patented Nov. 21, 1944 DEVICE FOR SIMULTANEOUSLY TUNING OSCILLATORY CIRCUITS Jan van der Heem, The Hague, Netherlands, assignor, by mesne assignments, to Hartford National Bank and Trust Company, Hartford,

Conn., as trustee Application July 22, 1941, Serial No. 403,564 In the Netherlands October 16, 1940 2 Claims. (Cl. 250-40) This invention relates to the simultaneous tuning, i. e., by means of equal and synchronous means capable of being set by a single operating member, of two oscillatory circuits whose resonance frequencies must differ by a constant value. Such a tuning device is used, for example, in superheterodyne receivers in which the input circuit or circuits, hereinafter briefly referred to as the preselector, must be tuned to the signal frequency whilst the local oscillatory circuit must be tuned to a frequency which relative to the signal frequency exhibits a difference equal to the intermediate frequency to which the remaining portion of the apparatus is tuned. The preselector of a superheterodyne receiver also frequently utilises a circuit which must be tuned to the mirror image of the desired signal and whose resonance frequency relative to the signal frequency must consequently have a difference equal to twice the intermediate frequency for which the ap.

paratus concerned is designed.

The invention more particularly relates to the obtainment of a constant frequency difference between the tuning of two oscillatory circuits tunable with the aid of equal means capable of being set in the same manner, the tuning of these circuits being effected by varying the position of cores of magnetic material relative to the coils so as to vary the inductance active in the circuits.

Since the inductance variation with a displacement of the magnetic core is obtained by the variation of the magnetic permeability of the medium comprised by the coil, this'manner of tuning of an oscillatory circuit is frequently referred to as permeability tunning. This term will also be used hereinafter to refer to the tuning method embodying the invention.

With the known methods of obtaining tuning with constant frequency difference use is made of variable elements which for both circuits give the same variation of the magnitude to be varied and, further, auxiliary elements are included in one or in both circuits, which permit of equalizing the frequency difference to the desired value in at least a certain number of positions of the synchronous tuning means, whilst in the intermediate positions small differences are permissible. Such circuits are known, for example, from Dutch patent specification No. 41,633 for circuits tuned by means of synchronous variable condensers. In principle, similar circuits may, of course, be developed for circuits tuned by means of synchronous permeability tuning. However, these circuits have the drawback that a great many circuit elements must be used, and furthermore, the correct adjustment to the desired difference frequency for all frequencies in thetuning range is not obtained.

Now, the invention provides a device for simultaneously tuning two oscillatory circuits,

which the synchronism is absolute.

whose resonance frequencies must differ by a constant value, by means of slidable, equal magnetic cores, in which auxiliary elements for adjusting the synchronism are not required and in According to the invention, for this purpose use is made of coils having equal winding widths which are at most equal to the length of the magnetic core, but in which the winding density of at least one of the coils is not constant. The term winding density is to be understood in this case to mean the number of turns per unit of length, measured in the direction of the axis of the coil.

The invention will be explained more fully by reference to the accompanying drawing, of which Figs. 1, 2 and 3 relate to the fundamental solution of the problem underlying the invention and Figs. 4 and 5 are diagrams showing the use of the invention.

Fig. 1 shows diagrammatically the longitudinal section of a coil having a winding width b constituted by n turns which are wound with constant winding density on the coil bush I. In the latter a magnetic core 2 is movable which is preferably a little longer than the winding width b. If now, the core is pushed into the coil (for example in the direction of the arrow in Fig. 1) the inductance will at first increase slowly when the core is not far pushed-in and subsequently increase more rapidly until the front of the core has approached the centre of the coil. After that, the increase gradually decreases again and at last becomes zero at the moment in which the centre of the core coincides with the centre of the coil. If, then, the core is pushed-in still farther the inductance decreases again. The foregoing is shown diagrammatically in curve I of Fig. 3, in which on the horizontal axis is indicated on an arbitrary scale the position k of the core relatively to the coil, whereas on the vertical axis, likewise on an arbitrary scale, commencing at the value 1, is shown the ratio between the inductance L with pushed-in core and the inductance Lo of the coil without core.

If, however, the coil is wound with a nonuniform Winding density the inductance variation exhibits a quite different curve on inserting the magnetic core, since the field intensity in the axis of the coil will vary i a manner different from that in the coil with constant winding density. One form of construction of a coil having a nonuniform winding density is shown in Fig. 2 in which the coil bush is again indicated by l and the magneto core by 2. The coil with the wind ing width b is now built up from a certain number of sections of tightly wound wire, the spaces 8 between the various sections being constant but the sections themselves comprising difierent numbers of turns. In the drawing the sections comprise successively 1, 2, 3 (k-l) k turns. Of

course, the inventionisnot limited to the said order of numbers ofturns. The number of sections and the series of the numbers of turns in each separate case are determined in accordance with the inductance variation" required. It is alternatively possible to obtain" anoneunifo'rm" winding density in a manner other than that'consisting in winding sections of' diiierent-numberss of turns, for example by making the -numbers oi turns of the sections as Well as' the spaces-between the sections different, or by winding with a variable pitch. It is evident: that: all-:1 these: forms of construction fall under the-scope.-oi.:

the invention.

The inductance variation during the insertion of the magnetic core into a coil accordingto 2in' the direction indicated by the arrowis repcore has, passed already" along the centre of'tlie coil, whilst the maximum value of the inductance is. only obtained when the core-:is-agaim pushed outof the coil; v

If the coils are to be usedfor thesimultaneous tuningby the same. movement of the magnetic cores of twooscillatory'circuits whoseiresonance frequencies must diiier by"a;.constant value; it appears. from Fig. 31that. only a portionof'the totalf possible inductance variation of" the coils can be used '(according to Fig. 3' approximately up. to theposition, k1- of..the. cores since beyond a..definitepositionwthe measures of the inductances. variationswno, longer... exhibit the required curve: In fact, the.inductancewhichyaried most rapidly before the .critical-Zposition-was obtained, varies beyond this position. moresl'owly. thanthe other which varied. the slowest before v.the..criti-.- cal position. To. obtain the .maximum. useful range, it is -consequently.-desirable. that not one, but both. coils. should b made with a. non-uni, form. winding density, inwhich. case. thevariation :of the densities must, .of. course; be. different.

Fig.4 showsdiagrammatically the use. of adsviceraccording to the invention in a superheteroe dyne receiver. In-this figure, llLindicates amixing tube, of which: one .grid has supplied .to. it the signal oscillation having. :atfrequency' fs and another grid the auxiliary oscillation having a frequency. is generatedbythez-local. oscillator, while-"the oscillation: having a frequency fur, being the differencesbetween fa andzfsgistakenirom theanodes. Thezsignalcircuit=or:preselection-.circuit; which-is supplied in someway or other'by th aerial l8, is'constitutedby the.coil1 H whose inductance may bevaried bY-"mQaIISJ'Of'"thGi-Slid? able magnetic core' l3, andthe condenser |2.-

The circuit for the auxiliary oscillationisrcon'e stituted by the coil l 4; whose inductance may be varied by means of the magnetic core- I63 and. the condenser" l5. ll shows diagrammatically a member by means'ofwhich' the cores l3 and l6 areipushed imultaneously and-in the same man'- ner into: the associated coils;

When. the: apparatus is ;tuned-, it is necessary thatin any position" of the tuning means the condition is fulfilled that theidifferencebetween is audio is equal .to aconstantvaluefim. It'is usualthat f ishigher than. is so that then the condition fo,fs'=constant mustibe fulfilled: For adefiniterange of is; the ratiobetween .themaximum and minimum valuesis in this case larger itative reactance.

than for the corresponding range of f0. Consequently, the inductance variation in the circuit ll; I2, I3 must be larger than that'in the circuit l4, l5, 16, while in the latter this variation has to take place less rapidly than in the firstmentioned'circuit. It appears from Fig. 3 that with'the use of a coil of Fig. 1 in the preselection circuit'and a coil ofcFig. 2 in the circuit of the localoscill'ator these conditions can be satisfied.

Another application Of a device according to the'invention is shown diagrammatically in Fig. 5'l"which shows;aipreselector for a superheteroclyne -apparatus comprising special means for the suppression of the image frequency. In this figure, I8, is the aerial which supplies the signal to a'preselectorand Ill is themixing'tube which suppliesan oscillation of the intermediatefrequency fm. Between the signal grid andthe cathode of'the tube- I0 is connected aseries resonant circuit 22, 25 which is tunable by means of the magnetic core 23'. Thiscircuit is-tuned to theimage frequencyof the signal'frequencyf5, i. e., to'the frequency fs+2fm.- For the'frequencyfsthe circuit 22, 23, 25behaves as a capacthe'coil 20; togetherwith the magnetic core 2!, is tuned to the signal frequency'js, so that, the signalof this frequency is transmittedwith'the highest possible intensity to the input grid'of the mixing tube. The inductancesof'the coils Zlland 22'- are varied by means: of, a member '24 which displacesihe' two cores'zl and 23 in the same manner. However, inorder'to satisfy the condition that the. parallel circuit and the series. circuit must exhibit a constant frequencyrdifierence, thesaid inductances must be. variedin different manners. and; to difierent exte'nts,.which may be obtainedby utilising a. deviceaccording to. the. invention.

What I claimis:

1. In a device for-simultaneously tuning. apluralityof oscillatory circuitsto resonant frequencies differing-by a substantially constant amount throughout the--tuning range. of the device; the combination of a; plurality, of tuning coils: and movable magnetic cores slidablewithin .theooils for varying the inductance thereof, each of :said coils. having substantially the same. diameter. and winding width and at least'one of said. coils-hay.- ing a winding comprising three'winding sections, each winding section being'spaced from the: adjacently positioned winding section .by a constant amount and having'an inductance;progressively larger than the adjacently -positioned:winding section the: winding width. of saidrcoil being. less than the; length oftthe associated. .core.

2. In:a .devicefor simultaneously tuning 31117111.- rality of oscillatory circuits to resonantfrequencies difiering by asubstantiallyconstant amount throughout the tuning range'of'thedevice, the combinationof a. plurality of'tuning: coils and movable magnetic cores slidable within the'coils for varying the inductance thereof, said coils comprising single layer solenoids having substantially the same-diameter and windingwidth and at least-oneof said coils having-awindingcomprising threewinding sections; each winding-section being-spaced from the adjacentlypositioned' By; means of this reactance' 

